We propose a 3-year study of free-living baboons, Papio ursinus, in Botswana. Omnivorous ground dwelling primates including some populations of man show marked preferences for certain kinds of food items. We will evaluate a series of hypotheses concerning the optimization of dietary intake by an omnivorous social primate. Our hypotheses concern the procurement of a calorically sufficient and nutritionally adequate diet in social context and in a fluctuating natural environment. We will assess the nutritional status of wild baboons through proximate analyses of foods, estimation of food intake, and from known values for digestibility and nutritive value of foods. These analyses will be related to ongoing studies of baboon food preferences at the California Primate Research Center. We will obtain nutritional profiles for selected individual animals in at least two baboon troops to test hypotheses concerning: (1) the role of animal matter in the baboon diet, with special reference to the energy and protein contributions of animal matter to the diet, (2) changes in the nutrition of female baboons under conditions of pregnancy and lactation, and the possible influence of maternal nutrition on infant survival, (3) the relationship of nutrition to social organization, in particular to differential access to resource by dominant and subordinate troop members and dietary differences between age/sex groups. Similarities in the nutrition of man and captive baboons are extraordinary. Baboons offer an optimal model of human nutrition under evolutionarily relevant conditions. This study may provide a comparative basis for human dietary norms, especially for meat intake.